This invention relates to deposition of materials and more particularly to a method and apparatus for introducing a controlled flow of vapor from a vapor source into a low pressure chemical vapor deposition reactor.
The deposition of thin films from vapor sources is a precision operation requiring controlled and precise introduction of a reactive gas or gases into a reaction chamber. The transmission of this vapor from its source to the reaction chamber generally has required a series of procedures. First of all, the source material from which the vapor is derived is heated to its sublimation temperature. This is generally performed within a sublimation chamber as known in the art. Secondly, the vapor so produced then must be mixed with a carrier gas for transport to the reaction chamber. Finally, the vapor and carrier gas mixture, maintained at relatively high pressure, must be introduced into the low pressure reaction chamber. The attendant gas carrier must be disposed of, and the vapor deposition process then occurs. Among other deficiencies, this method suffers from the problem of heat transfer through several interfaces and relying on the temperature being constant. While it is operative with liquid sources which generally have good thermal transfer characteristics, solid sources, particularly in powder form, have thermal gradients which are too large to allow any precision of material transfer.
As is evident from the above discussion, a need exists for more effective and direct methodology in the production and delivery of vapor to a low pressure deposition reactor. It is therefore an object of the instant invention to produce vapor from a source material in a controlled manner yielding controlled pressure. It is likewise an object of this invention to controllably transfer the vapor so produced into the vapor deposition reactor in a controlled manner via transmission means. It is a further object of this invention to maintain the vapor in that state without condensation thereof during transfer to the reactor. Yet another object of the invention is to transfer and deliver this vapor in a pure state and not mixed with any carrier medium. These and other objects will become apparent in the text which follows.